I just had all of the spark plugs replaced and ever since the engine hasn't been acting right. When i drive for a few miles and i reach my destination my car idles really funny. The RPM's fluctuate between 1 and a half all the way down to near stalling. It has stalled a couple times while i was in park. The car used to idle at a fixed position, but now the engine almost stalls if i just sit there without touching the throttle. Does anybody have an idea of what is going on?